Eric Flint & Harry Turtledove are two of the best known. I have only read a single two-book series by Flint, which was interesting at first and got lost the further from history it got. His primary series seems focussed on time travelers going back to the 30-years war, while the one I read was a more classical alternate history which diverged with an historical figure playing a bigger part in the War of 1812, and altering the outcome of the war.

Robert Conroy is another author who has written a number of divergent scenarios, but I am not a fan of his writing style. His books are usually titled after the year in which they take place, making it pretty easy to figure out his topics (ie. 1862, 1945 and so on).

Turtledove writes a number of diverse works in the genre, including a series that starts with a small change altering the outcome of the Civil War, and follows the new timeline all the way down to 1945, with the USA & CSA involved in the World Wars. His most famous (and possibly best) work is the standalone novel "Guns of the South" where time-travelers provide Robert E Lee & his army with modern automatic weapons. Other series have included an alternate World War 2 scenarios, including a two-parter with the Japanese invading Hawaii on Pearl Harbor day, a Nazi resistance movement to Allied occupation in a parallel to the contemporary war in Iraq and a longer series wherein World War 2 is interrupted by an alien invasion bent on conquering & colonizing the world, in 1942, forcing Nazis, Soviets, Allies etc to cooperate to defend the planet. He is currently in the middle of a four book (so far) series about a World War Two that starts at Munich in '38.

There are also several books by Newt Gingrich & William R Fortschen. There was "1945" about a WW2 where the US only fought Japan and now the Nazis rule Europe and prepare a simultaneous invasion of Britain and a raid on the US atomic bomb project. That was published around the time the author became Speaker of the House but never went anywhere, despite supposedly being the first of a series. There was also a trilogy about an alternate outcome to the Battle of Gettysburg, and a two-parter about a more serious & destructive attack on Pearl Harbor that also petered out without going anywhere. These authors, despite some problems with their characterization and plots, are among the more realistic and statistically & technically accurate.

SM Stirling wrote a trilogy which is more sci-fi than alternate history, but takes place mostly in the past, about an anti-America of slave-owners & plantations that is established in Africa at the same time as the US, and chronicles the rise of an equal but inimical world power, that ends up facing the USA in a post-WW2 Cold War, that features colonization of the whole solar system & genetic engineering, all in the 20th century.

Peter G Tsouras has also written alternate history novels, but they read more like speculative historical essays. He has, however, written two books so far in a series about the British Empire joining the American Civil War on the side of the Confederacy, which are more typical fiction novels.

Finally, there is a tetrology by Thomas Harlan, featuring a Roman Empire in a world that never had Christianity, but did have commonly-used magic, and which features an intact Western Empire in the seventh century AD. Among the historical characters featured are the historical Persian & Byzantine figures of the time, with other historical figures given much different roles as befits their altered timeline, such as Mohammed and Pope Gregory the Great.

As I said, what alternate history you read depends on what you are interested in. It should be sort of obvious from my readings which I have focussed on, but these are also among the favorite eras of the History Channel and Hollywood, so they would naturally draw the greatest number of history buffs.